1. Field of the Invention
The present disclosure relates to a DC plasma assisted chemical vapor deposition (CVD) apparatus in the absence of a positive column, a method for depositing a material in the absence of a positive column, and a diamond thin film fabricated by such method.
2. Description of the Background Art
Nano-crystalline diamond (NCD) thin films are being deposited by using the conventional apparatus for depositing a micro-crystalline diamond (MCD) thin film. However, a depositing variable different from the conventional variable for depositing an MCD thin film is being used, which may cause a depositing process to be unstable and a thin film to be non-uniform. Accordingly, the conventional apparatus and method for depositing an MCD thin film have to be considerably transformed.
The MCD thin film and the NCD thin film have been deposited by a microwave plasma CVD method and a hot filament CVD method. Using the microwave plasma CVD method, it is not possible to deposit a thin film having a large area and a microwave is not easily manipulated. Using the hot filament CVD method, a thin film having a large area is easily deposited and the fabrication cost is reduced due to employing a simple thermal decomposition process. However, since filaments are used, inconvenience may be caused, impurities may be introduced, and problems may be caused due to the thermal deposition process itself. In order to overcome these problems, new methods are required.
The present inventors devised an apparatus for depositing a diamond thin film by using a DC plasma as disclosed in U.S. Pat. Nos. 6,786,176 and 6,399,151. In this apparatus, a DC voltage is applied between two facing electrodes thus to generate a plasma therebetween. A substrate is disposed on an anode and an MCD thin film is deposited on the substrate. The DC plasma assisted chemical vapor deposition (CVD) apparatus has a simple structure, and deposits a material on a substrate with a large area. However, the apparatus for depositing an MCD thin film may encounter several problems when being applied to a method for depositing an NCD thin film. Accordingly, a new apparatus having advantages of the apparatus disclosed in U.S. Pat. Nos. 6,786,176 and 6,399,151 and useful for depositing an NCD thin film is required.
In a conventional method for depositing an NCD thin film by using a DC plasma (U.S. Pat. No. 6,042,900), a substrate is positioned below an grid-shaped anode, and a plasma is generated above the anode. This method has the advantages that overheating of the substrate is prevented and a non-conductive substrate can be used. However, the method has a limitation in that the anode has to be grid-shaped. That is, it is difficult to water-cool the anode and thus difficult to enhance the power density. Furthermore, a shadowing effect of the grid-shaped anode occurs between the plasma and the substrate, that is, a grid pattern remains on the deposited thin film. Accordingly, an apparatus for uniformly depositing a film without a grid pattern is required.
In another conventional method for depositing an NCD thin film by using a DC plasma (Gouzman et al, Diamond and Related Materials 7 (1998) 209-214), a substrate is mounted on a cathode, not on an anode. However, this method has a disadvantage in that the thin film may be degraded due to ion collision. Moreover, in this method, the anode is ring-shaped, which prevents the uniformity of deposition for large-area.
Accordingly, an apparatus for depositing an NCD thin film having two electrodes facing each other in which a substrate is mounted on an anode and the anode does not have a ring shape but can have a disc shape is required.